Online and other electronic advertising allows advertisers to display advertisements (or ads) to users, including those who are potential customers. For example, a publisher webpage can include one or more opportunities for inserting advertisements from third-party advertisers (e.g., space for a banner advertisement across the top of the webpage, spaces for advertisements along the sides of the webpage, native ads, overlays, etc.). When a user device (e.g., a computer running a web browser) processes a webpage for display, the user device can request an advertisement for one of the advertising opportunities on the webpage from an ad system. The ad system can select an advertisement for display within the area of the webpage associated with the advertising opportunity. For example, the ad system can select, based on information about the user, a banner ad from a particular advertiser from a set of multiple banner ads from multiple advertisers for display to the user in the banner ad space of the webpage. In some applications, ad systems can set cookies on user devices to track user behavior and facilitate determining the most relevant ad to display to the user.
Some web browsers do not allow third-party cookies, which can block ad systems from setting cookies on their own domains. As an example, a browser on a user device visits abc.com in response to a user entering “www.abc.com” into the address field of the browser, and the browser can request a webpage from the web server on abc.com. The web server on abc.com can return a webpage to the browser, along with cookie data to be set as a cookie on the domain “abc.com.” The cookie data from abc.com can be referred to as a first-party cookie, and many browsers will store the data as a cookie on the abc.com domain. The webpage source can include references to resources on other domains, such as an HTML image tag with a source address on another domain, e.g., xyz.com. The browser can request the image from a server on xyz.com and the server on xyz.com can return the requested image to the browser, along with data to set as a cookie on the domain “xyz.com.” The cookie data from xyz.com can be referred to as a third-party cookie. If the browser is configured to block third-party cookies, the browser will not store the data in a cookie on the xyz.com domain, until the user explicitly navigates to the xyz.com domain, e.g. by clicking on a link pointing to that domain.
As noted above, some ad systems provide data to user devices (e.g., data that when provided back to the ad system allows the ad system to identify the user devices) for storage as cookies. However, some web browsers do not permit setting third-party cookies, and require the user to visit the ad system's domain directly (e.g., by typing the ad system's URL into the address bar) for the ad system to set a cookie on the ad system's domain.